1. Field of the Invention
The present invention relates to multifocal ophthalmic lenses, lens designs, lens systems, and eyewear products or devices utilized on, in or about the eye. More specifically, the present invention relates to multifocal ophthalmic lenses, lens designs, lens systems, and eyewear products which, in most cases, reduce unwanted distortion, unwanted astigmatism, and vision compromises associated with Progressive Addition Lenses to a very acceptable range for a wearer.
2. Description of the Related Art
Presbyopia is the loss of accommodation of the crystalline lens of the human eye that often accompanies aging. This loss of accommodation first results in an inability to focus on near distance objects and later results in an inability to focus on intermediate distance objects. The standard tools for correcting presbyopia are multifocal ophthalmic lenses. A multifocal lens is a lens that has more than one focal length (i.e. optical power) for correcting focusing problems across a range of distances. Multifocal ophthalmic lenses work by means of a division of the lens's area into regions of different optical powers. Typically, a relatively large area located in the upper portion of the lens corrects for far distance vision errors, if any. A smaller area located in the bottom portion of the lens provides additional optical power for correcting near distance vision errors caused by presbyopia. A multifocal lens may also contain a region located near the middle portion of the lens, which provides additional optical power for correcting intermediate distance vision errors. Multifocal lenses may be comprised of continuous or discontinuous surfaces that create continuous or discontinuous optical power.
The transition between the regions of different optical power may be either abrupt, as is the case with bifocal and trifocal lenses, or smooth and continuous, as is the case with Progressive Addition Lenses. Progressive Addition Lenses are a type of multifocal lens which comprises a gradient of continuously increasing positive dioptric optical power from the far distance zone of the lens to the near distance zone in the lower portion of the lens. This progression of optical power generally starts at or near what is known as the fitting cross or fitting point of the lens and continues until the full add power is realized in the near distance zone of the lens. Conventional and state-of-the-art Progressive Addition Lenses utilize a surface topography on one or both exterior surfaces of the lens shaped to create this progression of optical power. Progressive Addition Lenses are known within the optical industry when plural as PALs or when singular as a PAL. PALs are advantageous over traditional bifocal and trifocal lenses because they can provide a user with a lineless, cosmetically pleasing multifocal lens with continuous vision correction and no perceived image break as the user's focus transitions from objects at a far distance to objects at a near distance or vice versa.
While PALs are now widely accepted and in vogue within the United States and throughout the world as a correction for presbyopia, they also have serious vision compromises. These compromises include, but are not limited to, unwanted astigmatism, distortion, and swim. These vision compromises may affect a user's horizontal viewing width, which is the width of the visual field that can be seen clearly as a user looks from side to side while focused at a given distance. Thus, PALs may have a narrow horizontal viewing width when focusing at an intermediate distance, which can make viewing a large section of a computer screen difficult. Similarly, PALs may have a narrow horizontal viewing width when focusing at a near distance, which can make viewing the complete page of a book or newspaper difficult. Far distance vision may be similarly affected. PALs may also make it difficult for a wearer to play sports due to the distortion of the lenses. In addition to these limitations, many wearers of PALs experience an unpleasant effect known as visual motion (often referred to as “swim”) due to the distortion that exists in each of the lenses. In fact, many people refuse to wear such lenses because of the discomfort from this effect.
When considering the near distance optical power needs of a presbyopic individual, the amount of near distance optical power required is inversely proportional to the amount of accommodative amplitude (near distance focusing ability) the individual has left in his or her eyes. Generally, as an individual ages the amount of accommodative amplitude decreases. Accommodative amplitude may also decrease for various health reasons. Therefore, as one ages and becomes more presbyopic, the optical power needed to correct one's ability to focus at a near distance and an intermediate distance becomes stronger in terms of the needed dioptric optical power. The near and intermediate distance optical power is usually stated in terms of an “add power” or “additive optical power”. An add power is the amount of optical power over the far distance vision correction. Add power usually refers to the optical power added to the far distance vision correction to achieve proper near distance vision correction. For example, if one has −1.00D of optical power correction for far distance viewing and +1.00D of optical power correction for near distance viewing such an individual is said to have +2.00D of near distance add power.
By comparing the different near distance add power needs of two individuals, it is possible to directly compare each individual's near point focusing needs. By way of example only, an individual 45 years old may need +1.00D of near distance add power to see clearly at a near point distance, while an individual 80 years old may need +2.75D to +3.50D of near distance add power to see clearly at the same near point distance. Because the degree of vision compromises in PALs increases with dioptric add power, a more highly presbyopic individual will be subject to greater vision compromises. In the example above, the individual who is 45 years of age will have a lower level of distortion and wider intermediate distance and near distance vision zones associated with his or her lenses than the individual who is 80 years of age. As is readily apparent, this is the complete opposite of what is needed given the quality of life issues associated with being elderly, such as frailty or loss of dexterity. Prescription multifocal lenses that add compromises to vision function and inhibit safety are in sharp contrast to lenses that make lives easier, safer, and less complex.
By way of example only, a conventional PAL with a +1.00D near distance add power may have approximately 1.00D or less of unwanted astigmatism. However, a conventional PAL with a +2.50D near distance add power may have approximately 2.75D or more of unwanted astigmatism while a conventional PAL with a +3.25D near distance add power may have approximately 3.75D or more of unwanted astigmatism. Thus, as a PAL's near distance add power increases (for example, a +2.50D PAL compared to a +1.00D PAL), the unwanted astigmatism found within the PAL increases at a greater than linear rate.
More recently, a double-sided PAL has been developed which has a progressive addition surface topography placed on each external surface of the lens. The two progressive addition surfaces are aligned and rotated relative to one another to not only give the appropriate total additive near distance add power required, but also to have the unwanted astigmatism created by the PAL on one surface of the lens counteract some of the unwanted astigmatism created by the PAL on the other surface of the lens. Even though this design reduces the unwanted astigmatism and distortion for a given near distance add power as compared to traditional PALs, the level of unwanted astigmatism, distortion, and other vision compromises listed above still causes serious vision problems for certain wearers.
Other multifocal lenses have been developed which provide for the placement of continuous and/or discontinuous optical elements in optical communication with one another. However, these lenses have not realized an optimal placement and alignment of the continuous and/or discontinuous elements. These lenses have also failed to realize an optimal optical power distribution in the optical elements placed in optical communication. Therefore, these lenses typically have one or more perceived image breaks, prismatic image jump, cosmetic issues, surface discontinuities, poor vision ergonomics, and/or an optical power gradient that is too steep. These issues typically translate into visual fatigue, eyestrain, and headaches for a wearer of these lenses. These lenses have also failed to realize an upper far-intermediate distance zone, a far-intermediate zone having a plateau of optical power, and a intermediate zone having a plateau of optical power.
Therefore, there is a pressing need to provide a spectacle lens and/or eyewear system that satisfies the vanity needs of presbyopic individuals and at the same time corrects their presbyopia in a manner that reduces distortion and blur, widens the horizontal viewing width, allows for improved safety, and allows for improved visual ability when playing sports, working on a computer, and reading a book or newspaper.